This is a phase II trial to investigate the safety and efficacy of thymidine in combination with carboplatin in the treatment of recurrent malignant gliomas. The objectives of this study are: 1)To evaluate the response rate. 2)To evaluate the qualitative and quantitative toxicities. 3)To evaluate time to treatment failure. Thymidine is a naturally occurring nucleoside metabolite that preferentially kills neoplastic cells in vitro and induces complete and partial regression of a wide variety of human tumor xenografts, including malignant glioma. Prolonged infusions (5-29 days; 60-240 g/m2) produce brief responses in heavily pretreated patients, but are also associated with considerable myelotoxicity. Shorter infusions of about 24 hours maintain antineoplastic activity in the preclinical setting and are free of myelosuppression, even at very high cumulative doses.